CORStest: A simple CORS misconfiguration scanner

by do son · October 3, 2017

CORStest

A simple CORS misconfiguration scanner

Based on the research of James Kettle

CORStest is a quick & dirty Python 2 tool to find Cross-Origin Resource Sharing (CORS) misconfigurations. It takes a text file as input which may contain a list of domain names or URLs. Currently, the following potential vulnerabilities are detected by sending a certain Origin request header and checking for the Access-Control-Allow-Origin response header:

Developer backdoor: Insecure dev origins like JSFiddle or CodePen are allowed to access this resource
Origin reflection: The origin is simply echoed in ACAO header, any site is allowed to access this resource
Null misconfiguration: Any site is allowed to access by forcing the null origin via a sandboxed iframe
Pre-domain wildcard: notdomain.com is allowed access, which can simply be registered by an attacker
Post-domain wildcard: domain.com.evil.com is allowed access, which can be registered by an attacker
Subdomains allowed: sub.domain.com allowed access, exploitable if attacker finds XSS in any subdomain
Non-ssl sites allowed: A http origin is allowed access to a https resource, allows MitM to break encryption
Invalid CORS header: Wrong use of wildcard or multiple origins, not a security problem but should be fixed

Note that these vulnerabilities/misconfigurations are dependent on the context. In most scenarios, they can only be exploited by an attacker if the Access-Control-Allow-Credentials header is present (see -q flag).

Download

git clone https://github.com/RUB-NDS/CORStest.git

Use

usage: corstest.py [arguments] infile

positional arguments:
infile File with domain or URL list

optional arguments:
-h, –help show this help message and exit
-c name=value Send cookie with all requests
-p processes multiprocessing (default: 32)
-s always force ssl/tls requests
-q quiet, allow-credentials only
-v produce a more verbose output